The invention herein relates to certain improvements to a Stirling type engine, both in construction and in operating method, which improvements are particularly useful for small engines of low horsepower which are adaptable to utilizing either combustion or solar heat energy sources. By way of background, Stirling type engines have been known for over 100 years. In general principal, such engines comprise a cylinder containing a pair of pistons, one forming a displacer plunger or piston and the other forming a power takeoff piston, with a space between the two pistons.
The end of the cylinder at the displacer plunger is heated and either external or internal passages are provided for the movement of gas, i.e., air, between the heated end of the cylinder and the space between the plunger and piston, which space is commonly referred to as the "cold space".
The general operation of that type of engine involves a cycle comprising the steps of: First, the piston and the plunger separated to their maximum, with the cold space between them containing gas, such as air. Second, the piston moves up to compress the gas and to cause it to move into the hot end of the cylinder above the displacer plunger. Simultaneously the displacer plunger moves downwardly towards the piston, providing the space at the hot end of the cylinder to receive the gas from the cold space. Third, the gas, now heated in the heated end of the cylinder, expands and forces both the plunger and piston down for the power stroke of the piston. Lastly, the displacer plunger rises and the gas returns to the cold space. Thereafter the cycle is repeated.
Various timing linkages are provided for timing and controlling the movement of the plunger and the piston and for transmitting the power delivered by the piston. Engines of this type have also been built with multiple cylinders and pistons for increasing the power output.
This type of engine has the advantage of being able to use a variety of different types of fuel to provide the heat energy since the heat is applied to the outside of one end of the cylinder. Thus, a flame type combustion heater may be used utilizing natural or synthetic gases, or petroleum products, or virtually anything that will appropriately burn and provide heat. Moreover, the engine lends itself to being operated by solar heat, i.e., by concentrating the heat of the sun through appropriate mirrors and the like, upon the hot end of the cylinder for providing the necessary heat. Thus, this type of engine is adaptable with respect to the type of fuel used and because the heat is externally provided, substantially complete combustion can be obtained to thereby minimize the exhaust of pollutants into the air. The engine can be made virtually pollution free, particularly if solar operated.
This type of engine lends itself particularly for small horsepower needs, particularly where steady power demands are required as opposed to automotive type of uses where power demands are intermittent and rapid acceleration is required. Although acceleration can be achieved with this type of engine, it becomes relatively complicated to do so.
Although this type of engine has been available since the early Eighteen Hundreds, over the years it has fallen in disfavor and been replaced by internal combustion engines of the 4-cycle, 2-cycle or diesel types and only relatively recently, where engine caused pollution has been a matter of public concern and fuel costs have risen, has interest in this type of engine arisen. However, efforts to utilize this engine have produced relatively complex and expensive constructions.
Thus, the invention herein focuses on a Stirling type of engine which is modified in construction and operation to provide a steady power output at relatively low cost.